Easily adjustable scaffolding is desirable to increase construction worker productivity and reduce back strain on workers. Ideally, scaffolding should be constantly adjusted to a height that will permit workers to stand upright when working so that bending down or reaching above shoulder level is not necessary. If scaffolding is difficult to adjust, workers will be less likely to take the time to adjust their scaffolding to maintain an optimum working height. Liftable scaffolding that contains a mechanism for lifting itself is desirable.
Using a large span of scaffolding across the face of a building is desirable to eliminate the need for workers to make potentially dangerous changes between multiple platforms. Maintaining the scaffolding in a horizontal position across the entire span is important. Typically, scaffolding is supported by uprights near each end of the scaffolding. Changes must be made to the position of the scaffolding at each upright to change the overall height of the scaffolding. Therefore, when using multiple uprights to support the scaffolding, the scaffolding should move evenly up or down the uprights to maintain a horizontal position.
Such liftable scaffold systems should have a safety device in the event that the lifting mechanism fails. Such a safety device must prevent the scaffolding from falling if the lifting mechanism fails. The safety device should also be a passive system that requires no effort of the user to activate and will automatically prevent the scaffold from falling.
One method of providing a liftable scaffold is exemplified in U.S. Pat. No. 6,311,800. The scaffold has stationary members that have rack teeth protruding from them. The rack teeth protrude into an associated pinion between two opposing discs that define the sides of the pinion. The pinion is rotatably attached to a platform to be lifted. The two opposing discs hold rollers between them. The rollers spin freely. As the pinions are rotated, the rollers roll over the teeth and raise the platform.